Composition adapted to remove shellac



Patented a. 25, 1932 UNITED STATES PATENT OFFICE BORIS LOUGOVOY, OF NEW YORK, N. Y., ASS IGNOR TO CHADELOID CHEMICAL COMPANY, OF NEW YORK, N. Y., A CORPORATION OF WEST VIRGINIA COMPOSITION ADAPTED TO REMOVE SHELLAC No Drawing.

This invention relates to a removing composition adapted for softening finish made with shellac so that the shellac layer may be readily removed from wood or other surfaces on which it forms a hard protective coating. i In the present invention the object is to produce a composition which will attack and soften shellac coatings more effectively than the standard removers which, in many cases, consists of a mixture of benzol, acetone and In other solvents, with a small amount of wax. Benzol, which represents the main part of most of the commercial removers, is not a good solvent for shellac, nor is acetone. Methyl or ethyl alcohol are good solvents for 1a shellac when used alone but-in admixtures with'benzol or other hydrocarbons and particularly when wax is also present, their removing action on shellac is usually diminished according to the relative amount of hyfi l drocarbons present. The retarding action of such solvents as benzol in conjunction with alcohol usually results. in the slowing down of the initial action of the remover on the upper layer of the shellac coating.

When a coating of shellac on wood is new it is usually comparatively easily attacked by solvents. say during the first few weeks or maybe months, but gradually changes are produced in the coating due to the action of oxygen of the air and especially under influence of light. and the coating becomes more and more insoluble and a shcllaced surface which has been exposed to those conditions for a period of several years becomes very difficult to soften by the usual paint and varnish removers.

It is known that such an aged shellac surface can be comparatively easily removed by the application of strong aqueous solution of alkali, such as a strong solution of caustic soda. V

However when a solution of caustic soda is allowed to remain in contact with. wood for even a short time it acts on the wood fibres and usually producesa yellow and in many cases a dark brown coloration of the wood surface, which in most cases is a very undesirable result because usually an old coat of shellac is to be removed in order to replace the same by a fresh coat of shellac and Application filed November 30, 1928. Serial No. 322,970.

therefore any change in the color of thewood would be a disadvantage.

When an old shellac coating is acted upon by a solvent, the action of the solvent is slowed down especially on the surface layers of the coating, and if the outside oxidized insoluble layer is opened in one Way or another to penetration of solvent the softening of the under layers with the same solvent does not present any particular difficulty.

I have also found that very low concentrations of an alkaline substance soluble in the remover solvents will accomplish the action of opening the aged shellac surface. "l he alkaline substances which I prefer are caustic soda or caustic potash (sodium or potassium hydroxides) According to my observation the addition of a very small proportion of caustic soda to, for example, alcohol, when the latter is used in the preparation of paint and varnish removers, say in conjunction with benzol or with benzol and acetone, will greatly increase the cutting speed of such remover on a shellacked surface.

The mixture of two solvents, one of them being a wax solvent, such as benzol, and the other a wax precipitant, the latter containing a small proportion of caustic alkali, affords a valuable low-alkali-content solvent composition for use on shellacked surfaces. A suitable composition of this kind may be made by dissolving one part of caustic soda in anhydrous methyl alcohol and mixing with a solution consisting of two parts of parafiin wax in benzol, the methyl alcohol and benzol amounting together to 100 parts, and preferably the alcohol is in considerable excess over the benzol.

Any composition designed for use as a finish remover in addition to being effective on one or another kind of painted or varnished surface should also satisfy another important condition, that is, such a composition should possess the propert .of remaining wet for a sufiicient period 0 time for the solvents to exercise their dissolving power. For this purpose every composition of this nature, which is composed of light volatile solvents, should include an agent capable of retarding evaporation. Parafiin or ceresln waxes are the most suitable. However, even the addition of wax is not all that is necessary to stop evaporation. The relative volatility of each individual solvent, both penetrating and loosening, is of importance for the proper retardation of evaporation even in the presence of wax. It is true that by increasing the relative amount of wax in a remover it is possible to lessen the evaporation to a large extent, but on the other hand the more wax that is introduced into the removing composition the slower will be the removing action. Consequently the proportion of wax or other retarding agent is limited to an amount which will not decrease the efliciency of the removing composition beyond a reasonable limit. In general it is desirable to reduce the amount of the wax in a remover to the lowest possible limit consistent with a sufiicient degree of retardation of evaporation, and under those circumstances the infiuence of the boiling point-and vapor pressure of solvents at ordinary temperature play a very important role.

In order to explain this point it should be recalled that the action of wax in arresting evaporation is based on thefact that'when Wax is dissolved in a- .wax solvent, such as benzol, and this solution is diluted with a wax precipitant, such as an alcohol, the wax partially separates from the solution in the amorphous semi-colloidal state and forms on the surface a film or skin which is a true retarder of evaporation.

This surface film in order to be effective should be very strong and should possess the property of rebuilding itself quickly as soon as the continuity of such film is destroyed. Such conditions can exist under a proper equilibrium between the wax solvent and wax precipitants. If in the mixture of two solvents, one of which isv a wax solvent and the other is a wax precipitant, the first solvent evaporates faster than the second the relative amount of wax precipitant will in crease, thus creating a favorable condition for the formation of a stronger and more rapidly rebuilding film. On the other hand a quite opposite effect will be produced if in 4 the solution of the above two solvents the one which will serve as a wax precipitant evap- Under these conditions the relative proportion of wax solvent in the mixture will increase and a greater proportion.

of wax will remain in (or go into) solution, thus presenting a more unfavorable condition for a good surface film. According to my observation it is not necessary that the whole of wax precipitant be of lower volatility than the wax solvent. It generally sufiices to have a substantial part of such wax precipitating solvent less volatile than the wax solvent. The wax precipitant is frequently referred to in the art as the loosening solvent.

In connection with the present invention I have'observed that as a rule an alkali-containing mixture of benzol and methyl alcohol, which is a very effective shellac remover, has a higher rate of evaporation than the same mixture without alkali, and therefore in order to adjust the rate of evaporation to a highly satisfactory limit, for example, to a condition where preferably not more than about five per cent of the weight of the remover will be lost in twenty-four hours when the mixture is exposed to the air in an open dish at a room temperature of 7275 F., Imay add to the mixturea higher boiling solvent serving as a wax precipitant. When such solvent is introduced it is best to use one which by itself has a satisfactory solvent or loosening action on shellac.

In the table below is given the activity of different solvents on shellaced surfaces. This activity was determined in the following way: A piece of a panel of pine wood was coated with several coats of a solution of white shellac in anhydrous methyl alcohol. After the application of each coat it was thoroughly dried and the next coat applied thereto. Six such coats were used altogether. After the application of the last coat the panel was dried in an oven at 60 C. for twelve hours and then exposed. to the action of ultraviolet light for six hours. The panel was then cut into strips. Various solvents were placed in a series of test tubes and a strip of the above shellacked wood was placed into each test tube and the time was noted by a stop watch when the removing action was plainly visible. This removing action was represented by the number-of seconds which elapsed from the moment the shellacked strip was immersed in the solvent until the appearance of signs showing complete removing action. The results are tabulated below:

Action in seconds Complete Softening removing Single aolventa I Anhydrous methanol 15 100 Anhydrous ethanol 40 150 Isopropyl alcohol (98%) 130 300 Anhydrous acetone (pure, neutral) 70 120 Lnrmsnl 40 100 Methyl ethyl ketone 50 Methyl acetate 35 80 thy] acetate 70 150 Fnrfumi Very slow Benzol Very slow Dichlorbenzol 0 action Carbon tetrachloride"... No action Triehlorethvlene 55 Diaeetone alcohol No action Mesityl oxide 115 Anhydrous methanol-{4% KOH 5 to 7 About 50 Ethyl aleohol+1% KOH 90 Compound solvents Benzol-enhydrous methanol l5 80 Belize-ethyl alcohol 30 100 Benzo"-methanol+l% KOH 7 to 10 30 Benzo"-ethanol+1% KOH 15 40 Benw-lugosol 150 Benzol-lugosol-HZ, KOH. 35 100 Benzol-methyl acetate-.. 20 60 Benzol-ethyl acetate 60 180 til contact with such bodies as organic esters,

lln this case the alkali may be completely neutralized and the stability of the remover in storage will be destroyed. It therefore fol- I lows that all incompatible solvents which are apt to change unfavorably under the influence of caustic alkali should preferably be avoided...

Having described in general the property and preparation of the shellac remover composed of a removing solvent mixture and a compatible surface-opening agent, I will proceed now to give examples of various formulas for such removers. It is understood that all formulas given below should be regarded only as examples and that l. do not wish to restrict myself to the exact proportions or composition ofthese formulas. All these examples include a low percentage of paraffin Wax as an agent to retard evaporation of the solvent. ln this connection it should be mentioned again, as already pointed out, that the addition of various solids which are capable of dissolving in one of the solvents used in paint and varnish remover will result in the cutting down of the cutting speed of the giv- (in solvent or of the mixture of this solvent and other ingredients, and therefore the cut-- ting speed or rate of attack of the Wax-containing composition will be slower than the cutting speed of a corresponding mixture without wax. All proportions are given by weight.

Ewamplel Parts Benzol 30 Anhydrous methanol 5Q Lugosol (Ketone condensation products) 20 Paraifin wax 2 Powdered KOH 1 Loss in weight by evaporation at (1 part of NaOH may be substituted for the 1 part ofKOH, if desired.)

Ewample 3 Parts Petroleum naphtha.- Anhydrous methanol Isopropyl alcohol 5 Paraliin wax 2 Powdered NaOH 0 .9 Loss in weight by evaporation at F. in 2 hours 3.5% Loss in weight by evaporation at 75 F. in 24 hours 10% Removing power 120 seconds.

When removers given in above examples were tested in reference to their effect upon wood fibres, after removers had. penetrated all through the shellac coatings, it was found that no injurious effect on wood was produced. There was only a slight, easily removable staining, due to the formation of dyelike compound when caustic alkali is acting upon shellac.

It is known that caustic alkali acts chemically upon shellac, forming a violet-reddish colored soluble material; therefore when a remover containing caustic alkali is flowed upon a shellacked surface, such an alkali enters into a chemical combination with shellac, which results in progressive decrease in the amount of free alkali. From this it follows that the injurious effect of alkali upon wood fibres can be eliminated if all alkali is and therefore all alkali should be consumed by the shellac before the remover cuts through to the wood surface. This constitutes a notable difference in the removing composition discussed in the present specification as compared with compositions containing a higher proportion of caustic alkali. case there will remain a great excess of free alkali which is apt to injure the Wood surface, after all of the shellac coating is softened. On the other hand a remover containing just enough alkali only to open the surface will be but transiently alkaline after contact with such surface and'then becomes non-alkaline, or at least of an alkalinity below that of wood-discoloring strength, acting essentially by means of incorporated organic solvents,

thus preventing any possibility of direct contact of any material proportion of free alkali with wood fibres. Thus in the preferred form of the invention I use a proportion of surface-opening alkali just suificient to be substantially neutralized by the acids of shellac,.whereby the removing composition is In this latter,

reduced in alkalinity below wood-discolorin strength.

ith acetone a proportion of alkali may be used to form condensation products of a 5 solvent character (lugosol) and yet have sufficient alkali present to attack the insoluble surface layers of the shellac while limiting the maximum proportion below that of wooddiscoloringstrength after neutralization by the shellac acids. 4

By the term lugosol herein employed, I mean a product produced by adding a small quantity of alkali (say 0.02% of KOH) to v carefully neutralized acetone, well agitating the mixture, allowing to stand for about 18 hours or longer, neutralizing the alkalinity (preferably with an acid formin an insoluble potassium salt, e. g. tartaric distilling off unconverted acetone and filtering. This 20 liquid is a mixture having a boiling point range of about 60 to 170 C. This product has been referred to in some of my earlier cases.

It is of course appreciated that some of the solvents above referred to frequently contain substantial amounts of acid constituents,

and these acid constituents are preferably first removed from the solvents in a preliminary treatment, or the acidity is allowed for in addition to the 1% KOH above referred to. Without this preliminary neutralization or allowance for acidity of the 1 materials, a considerable part or even all of the 1% of alkali might be neutralized by acidity of the raw materials.

.1 What I claim is:

1. A removing composition adapted for use on shellacked surfaces and composed of a mixture of hydrocarbon wax solvent with a wax precipitant liquid consisting in major part at least of methyl alcohol and a volatile ketonic solvent, a few per cent of wax and approximately one per cent of caustic alkali as surface-opening agent.

2. ,A removing composition adapted for use on shellacked surfaces and composed of a mixture of hydrocarbon wax solvent, an alcohol, a ketonic solvent, few per cent of wax,

and about 0.9 to 1.0% of caustic alkali to open the surface and substantially neutralizable by the acids of shellac whereby the composi tion is reduced in alkalinity below Wood-discoloring strength, by the time it has penetrated the shellac coating.

3. A shellacremover comprising below 30% of petroleum naphtha, as its essential wax solvent, the other solvents therein being mostly methanol with a small percentage of a higher and less readily volatile alcohol, said remover containing a wax. and about 0.9% to 1.0% of a fixed caustic alkali.

In testimony whereof I afiix'my signature.

- BORIS N. LOUGOVOY. 

